The present invention relates to a motor type fuel pump and, more particularly, to a centrifugal motor type fuel pump arranged in an automobile fuel tank to supply fuel.
A conventional fuel pump of this type is arranged in a fuel tank and can prevent "vapor lock" caused by a high temperature of fuel more effectively than fuel pumps of other types. In addition, an installation space and a sealing structure need not be considered in this fuel pump. Conventional centrifugal motor type fuel pumps having different structures have been proposed. A typical conventional fuel pump of this type includes a substantially cylindrical armature housing with an upper closed end and a pump chamber housing. The armature housing accommodates an armature with a commutator, permanent magnets surrounding the armature, and a cylindrical stator with yokes. The pump chamber housing defines a pump chamber which receives a impeller. The impeller is fixed at the lower open end of the armature housing and driven by the armature. A pair of brushes are held in a brush holder in the armature housing and are biased to be in slidable contact with the outer surface of the commutator of the armature. External connection terminals electrically connected to the corresponding brushes run through holes formed in the armature housing or the like and are electrically connected to an external power source.
In this conventional centrifugal motor type fuel pump, fuel is drawn from a pump suction port formed in the pump chamber housing and is discharged from the pump chamber. The discharged fuel is guided to the upper end portion of the armature housing through spaces between the motor components such as the armature and the stator. Fuel is then fed to the engine through a discharge pipe.
In this fuel pump having the structure described above, however, fuel compressed in the pump chamber by suction through the suction port is guided to the upper end of the armature housing through small spaces between the motor components and is discharged through the discharge port. In this case, the small spaces cannot assure a sufficient fuel path area. In addition, fuel is directly stirred by a rotating member such as the armature to produce a flow resistance, and the fuel flow is disturbed by such rotation to form bubbles. This tends to pose problems such as vapor lock.
In order to solve these problems, in Japanese Patent Prepublication No. 58-160545 or Japanese Utility Model Publication No. 52-35521, a groove formed in a housing outside a stator is utilized as a fuel path running along the axial direction of the housing, or a groove formed in a holder integrally holding split permanent magnets is utilized as the fuel path. With these structures, a special groove must be formed to constitute a fuel path, which requires extra molding steps and increases the number of components. In addition, a sufficient path area cannot still be provided, and hence a proper discharge amount cannot be inevitably obtained.
Furthermore, a demand has also arisen for improving workability and assembly efficiency as well as compactness and light weight of the entire pump, in addition to the solution for the fuel path. Therefore, there is much room left to be improved.